The present invention relates to systems and methods for generating ultrasound images, and more particularly to systems and methods for generating ultrasound images without system contact to the patient, which may be achieved, for example, using photoacoustic energy and/or laser vibrometry.
Ultrasonic imaging techniques of body tissue and bone are well established in medical practices and aid physicians diagnosing diseases and injuries. Current systems rely on mechanical transducers and receivers in contact with the skin where coupling gels act as an interface to reduce the impedance between the device and skin. Conventional ultrasound images are obtained in a contact manner by using an ultrasonic transducer placed directly on the area of interest to send and receive the acoustic signals. In general, an acoustic pulse is emitted into to the body. Echoes from structures inside the body are reflected back to the transducer with the time of arrival providing information about the range to the structure. The acoustic source is omnidirectional, thus only range information is obtained, and a two-dimensional (2D) image is formed by using a line of transducers that yield information in the cross range direction.
However, considerable work is currently ongoing to form three-dimensional images via the scanning of the transducer line array. However, this presents registration error challenges as the individual 2D images must be aligned properly. Investigations are also ongoing to combine the individual source elements of 2D arrays of transducers in such a way that the transmitted energy has a directionality to obtain better quality spatial information. However, practical implementation of 2D arrays suffer from challenges in making a sufficiently large array that is conformal and uniformly coupled to the surface of interest (e.g. the human body).
Additionally, in certain circumstances, a noncontact operation for obtaining ultrasound images may be desirable. For example, in surgical situations where sterility is an issue, situations where direct contact is unpleasant or painful (e.g., imaging the eye), or emergency situations where the patient is in transit and/or being stabilized and may not be easily imaged via a contact system. Additional applications include, for example, real-time surgical feedback imaging, traumatic brain injury (TBI) detection, and bone health monitoring. Real-time surgical guidance and feedback could be improved from an imaging technique that can directly access exposed skin or traumatized tissue without contact, especially in very delicate procedures such as spinal and neck surgery.
One example approach includes photoacoustic tomography (PAT) which is an emerging optical technique. PAT is often used to image near surface shallow capillaries in animal tissue, for example, with typical penetration depths less than 1 mm. The PAT technique employs an optical source to cause the photoacoustic effect and contact transducers to record the response. Recent studies are exploring the laser Doppler vibrometer as a sensing device, thus making the system optical. In these studies, measureable signals are observed to depths of less than 1 cm in biological phantoms or natural tissue. However, for optical measurement systems to compete with practiced medical ultrasound, penetration depths of at least several inches are needed to probe structures of interest and, the light must be eye and skin safe.
Thus, there is a need for systems and methods capable of providing an efficient means for coupling acoustic energy into media in a noncontact manner to generate ultrasound images and, thereby, treatment of injuries such as TBI and bone fractures.